Mutual passivation of electrically active and isovalent impurities in dilute nitrides

Using first-principles calculations we investigate the mutual passivation of shallow donor Si and isovalent N in dilute GaAsN alloys. Instead of the recently proposed pairing of Si and N on adjacent substitutional sites (Si(Ga)-N(As)) [K. M. Yu et al., Nat. Mater. 1, 185 (2002); J. Li et al., Phys. Rev. Lett. 96, 035505 (2006)] we find that N changes the behavior of Si in dilute nitride alloys in a more dramatic way. N and Si combine into a deep-acceptor split interstitial, where Si and N share an As site [(Si-N) (As)], with a significantly lower formation energy than that of the Si(Ga)-N(As) pair in n-type GaAs and dilute GaAsN alloys. The formation of (Si-N)(As) explains the GaAs band-gap recovery and the appearance of a photoluminescence peak at approximately 0.8 eV. This model can also be extended to Ge-doped GaAsN alloys, and correctly predicts the absence of mutual passivation in the case of column-VI dopants.     

Hydrogen passivation and reactivation of shallow Zn acceptors in GaAs

We report on a study of the hydrogenation of melt-grown Zn-doped GaAs, using a remote DC plasma system. Depth profiles of the free carrier concentration revealed the extent of passivation of the hydrogenated GaAs. Annealing at temperatures between 90 and 160° C for various times, with a reverse bias applied to the Schottky diode, allowed us to observe the reactivation of the Zn-acceptors in the high-field space-charge region of the diode. The thermal dissociation of the electrically neutral ZnH complex is found to obey first-order kinetics, with a dissociation energy E_ZnH = 1.33 ± 0.03 eV.     

GaAs surface passivation by plasma-enhanced atomic-layer-deposited aluminum nitride

A low-temperature passivation method for GaAs surfaces is investigated. Ultrathin AlN layers are deposited by plasma-enhanced atomic-layer-deposition at 200 ° C on top of near-surface InGaAs/GaAs quantum well structures. A significant passivation effect is seen as shown by up to 30 times higher photoluminescence intensity and up to seven times longer lifetime compared to uncoated reference samples. The improved optical properties are accompanied by a redshift of the quantum well photoluminescence peak likely caused by a combination of the nitridation of the GaAs capping layer and a surface coupling effect.     

Magneto-optical study of shallow donors in transmutation-doped GaAs

Lineshapes and peak positions of 1s→2p^?1, donor transitions in epitaxial GaAs samples of relatively low compensation have been studied as functions of magnetic field by use of photoconductivity measurements. Some of these samples were produced by transmutation doping using thermal neutrons—a method which is useful for the controlled introduction of donor impurities in GaAs. Two new effects, tentatively attributed to van der Waals interactions between neutral donor atoms, are observed: (1) although both Se and Ge donors are introduced by thermal neutron transmutation, the Se line is much broader than the Ge line, and (2) deviations from isolated-donor behavior occur in the magnetic field dependence of the chemical shift of the shallowest donor present. The separation of lines from two deeper donors, Ge and Si, verified the simple phenomenological theory of the magnetic field dependence of central cell corrections of isolated donors up to at least 10T.     

Electroreflectance and photoluminescence measurement of passivation by hydrogenation in GaAs/AlGaAs structures

We have studied by electrolyte electroreflectance and photoluminescence a GaAs/AlGaAs resonant tunneling structure (RTS) with a highly n-doped GaAs cap, before and after hydrogenation. We measured the amount of passivation of shallow donor states and of deep traps in the cap and found the approximate pinning levels and interace charges of the RTS.     

GaAs surface passivation by ultra-thin epitaxial GaP layer and surface As-P exchange

The GaAs surface passivation effects of epitaxially grown ultra-thin GaP layers and surface As-P exchange have been investigated. Optical properties of passivated and unpassivated InGaAs/GaAs near-surface quantum wells (QWs) grown by metal organic vapor phase epitaxy (MOVPE) are studied by low-temperature continuous-wave and time-resolved photoluminescence (PL). By optimizing the growth conditions, smooth surface morphologies and significant improvement of optical properties were observed for both passivation methods. Passivation improved the PL intensity more than two orders of magnitude and notably increased the PL decay time.     

Reconstruction dependence of the etching and passivation of the GaAs(001) surface

The microscopic nature of the selective interaction of iodine with an As- and Ga-stabilized GaAs(001) surface has been investigated by the photoelectron emission and ab initio calculations. The adsorption of iodine on the Ga-stabilized (4 × 2)/c(8 × 2) surface leads to the formation of the prevailing chemical bond with gallium atoms; to a significant redistribution of the electron density between the surface Ga and As atoms; and, as a result, to a decrease in their binding energy. Iodine on the As-stabilized (2 × 4)/c(2 × 8) surface forms a bond predominantly with surface arsenic atoms. Such a selective interaction of iodine with the reconstructed surfaces gives rise to the etching of the Ga-stabilized surface and the passivation of the As-stabilized surface; this explains the layer-by-layer (“digital”) etching of GaAs(001) controlled by the reconstruction transitions on this surface.     

A comparison of the effectiveness of GaAs surface passivation with sodium and ammonium sulfide solutions

To explore the possibility of improving the effectiveness of chemical and electronic passivation, a study has been made of the properties of GaAs surface treated with solutions of inorganic sulfides [Na₂S and (NH₄)₂S] in various amphiprotic solvents (water, alcohols). X-ray photoelectron and photoluminescence spectroscopy shows that the efficiency of both chemical and of electronic passivation of GaAs surface increases with decreasing dielectric permittivity of the solvent. The degree of this increase reached with solutions of the sulfide of a strong base (Na₂S) is larger than that of a weak-base sulfide [(NH₄)₂S]. Fiz. Tverd. Tela (St. Petersburg) 39, 63–66 (January 1997)     

Dependence of impurity binding energy on nitrogen and indium concentrations for shallow donors in a GaInNAs/GaAs quantum well under intense laser field

Within the framework of the effective-mass approximation, using a variational method, we have calculated the effect of intense laser radiation on the binding energy of the shallow-donor impurities in a Ga_{1- x} In _x N _y As_{1- y} /GaAs single quantum well for different nitrogen and indium mole concentrations. Our numerical results show that the binding energy strongly depends on the laser intensity and frequency (via the laser dressing parameter) and it also depends on the nitrogen and indium concentrations. Impurity binding energy under intense laser fields can be tuned by changing the nitrogen and indium mole fraction.     

Excitonic fine structure of out-of-plane nitrogen dyads in GaAs

We report on the excitonic photoluminescence from a nitrogen dyad of C_2v symmetry located in a plane parallel to the emitted light wavevector (out-of-plane). We determine that the spectral signature of out-of-plane dyads is composed of five transitions linearly polarized along [1 0 0] or [0 1 0]. A sixth transition is in principle allowed but could not be observed due to its relatively low oscillator strength. However, a perturbation in the close vicinity of a dyad can significantly influence the fine structure and the polarization sequence of the emission and can bring out this sixth transition.     

Dynamics of the cascade capture of electrons by charged donors in GaAs and InP

The times for the cascade capture of an electron by a charged impurity have been calculated for pulsed and stationary excitations of impurity photoconductivity in GaAs and InP. The characteristic capture times under pulsed and continuous excitations are shown to differ noticeably both from each other and from the value given by the Abakumov–Perel–Yassievich formula for a charged impurity concentration greater than 10¹⁰ cm^–3. The cause of this difference has been established. The Abakumov–Perel–Yassievich formula for the cascade capture cross section in the case of stationary excitation has been generalized. The dependences of the cascade capture rate on the charged impurity concentration in GaAs and InP have been found for three temperatures in the case of pulsed excitation.     

Remarks on the theory of electron capture into shallow donors in GaAs

A new model for low-temperature recombination of conduction electrons to ionized donors in GaAs is proposed. It assumes that the conduction electron is captured into the ground state of shallow impurity by simultaneous emission of two LA phonons. From a comparison of computed capture rate with recent experimental results the estimated value of the two-phonon deformation potential is d_2LA = 0.02 eV.